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The Deepening Story of How Climate Change Threatens Human Health

Re-posted from the White House Office of Science and Technology Policy blog.

Climate change poses risks to human health through many pathways, some more obvious than others. Rising greenhouse-gas concentrations, driven by human activities, result in increases in temperature, changes in precipitation, increases in the frequency and intensity of some extreme weather events, and rising sea levels. These climate-change impacts endanger our health by affecting our food and water sources, the air we breathe, the weather we experience, and our interactions with the built and natural environments. As the climate continues to change, the climate-related risks to human health will continue to grow.

Today, building on the Third National Climate Assessment issued in May 2014, the Administration released a new report summarizing the growing understanding of how climate change is directly and indirectly affecting human health. The report, The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment, finds that “every American is vulnerable to the health impacts associated with climate change.” Drawing from decades of advances in the science of climate change and its influences on ecosystems and human society, the report strengthens our understanding of the significant threat that climate change poses to the health of all Americans and highlights factors that make some individuals and communities particularly vulnerable.

Among the new assessment’s specific findings is the projection that, under mid-range growth of global greenhouse-gas emissions, the combination of resulting summer temperatures in the United States and the known physiology of human sensitivity to heat would result in an increase of thousands to tens of thousands of premature heat-related deaths per year by the end of the century. Extreme heat poses a particular risk for children, the elderly, disadvantaged and socially isolated groups, and even people taking some prescription drugs that may impair the body’s ability to regulate temperature. The increase in heat-related deaths in most regions is expected to outweigh any reduction in cold-related deaths from warmer winters.

Changes in the climate also affect air quality. Human-induced climate change has already made conditions more favorable for ground-level ozone pollution – the key component of smog – in some regions of the United States. Higher temperatures increase the rate at which ozone forms, and associated changes in meteorological conditions can lead to stagnation events where large pockets of still air allow pollution levels to accumulate over a region. These effects are especially concerning when combined over urban areas. Unless offset by additional emission reductions of ozone-forming pollutants, these climate-driven increases in ozone will cause increases in premature deaths, hospital visits, lost school days, and acute respiratory symptoms.

Rising temperatures and hotter, drier summers are projected to increase the frequency and severity of large wildfires, especially in the western United States (see Figure 1). Wildfires emit fine particles and ozone-forming pollutants that in turn increase the risk of premature death and adverse chronic and acute cardiovascular and respiratory health symptoms. Firefighters, in particular, are exposed to significantly higher levels of combustion products from fires.

Figure 1. Based on 17 climate model simulations for the continental United States using a higher emissions pathway (RCP8.5), the map shows projected percentage increases in weeks with risk of very large fires by mid-century (2041-2070) compared to the recent past (1971-2000). The darkest shades of red indicated that up to a 6-fold increase in risk is projected for parts of the West. This area includes the Great Basin, Northern Rockies, and parts of Northern California. Gray represents areas within the continental United States where there is either no data or insufficient historical observations on very large fires to build robust models. The potential for very large fire events is also expected to increase along the southern coastline and in areas around the Great Lakes. (Figure source: adapted from Barbero et al. 2015 by NOAA)

A changing climate is also affecting the seasonality and geographic ranges of vector-borne diseases – such as Lyme disease and West Nile virus, which are transmitted, respectively, by ticks and mosquitoes. Between 2001 and 2014, both the distribution and number of reported cases of Lyme disease increased in the Northeast and Upper Midwest (see Figure 2). The assessment found that vector-borne pathogens of a number of kinds are likely to emerge or re-emerge due to the interactions of climatic factors with many non-climatic drivers, such as changing land-use patterns and human population density.

Figure 2. Maps show the reported cases of Lyme disease in 2001 and 2014 for the areas of the country where Lyme disease is most common (the Northeast and Upper Midwest). Both the distribution and the numbers of cases have increased. (Figure source: adapted from CDC 2015)

The assessment also highlights the disproportionate impacts of certain other climate-change-related health issues on certain communities. Indigenous people, for example, face decreasing access to traditional wild and cultivated foods, which have both health and cultural implications for these communities. And warming can exacerbate shellfish disease and make mercury more readily absorbed into fish tissue, posing a particular hazard to indigenous communities that consume above-average quantities of fish and shellfish.

The assessment highlights how climate change can exacerbate existing health risks, but also create heath threats in new locations or new times. Some threats will occur over longer time periods, or at unprecedented times of the year. For example, increases in water temperature will alter the geographic range and seasonal window of growth for harmful bacteria and algae, exposing more people in more places. Changes in temperatures, precipitation, and extreme events such as flooding are also expected to increase risk of foodborne illnesses from pathogens like Salmonella and E Coli.

Impacts on people’s physical health can also affect their mental health. In addition, many people exposed to extreme weather events experience serious mental health consequences, including post-traumatic stress disorder, depression, and anxiety. The mental health impacts of hurricanes, floods, and drought can be expected to increase as more people experience the stress—and often trauma—of these disasters.

Reducing the health risks from climate change is a top priority for President Obama and will be a key benefit of implementing his Climate Action Plan. The information about those risks contained within this new assessment should be a strong additional impetus for decision-makers across the Nation to support all three elements of the Plan—reducing domestic emissions of the carbon pollution that is driving global climate change, investing in measures to increase preparedness and resilience against the changes in climate that occur, and working with other nations around the world to encourage and help them to do the same.

John Holdren is Assistant to the President for Science and Technology and Director of the White House Office of Science and Technology Policy.

Gina McCarthy is Administrator of the U.S. Environmental Protection Agency.

Vice Admiral Vivek Murthy is the U.S. Surgeon General.

Kathryn Sullivan is Under Secretary of Commerce for Oceans and Atmosphere and Administrator of the National Oceanic and Atmospheric Administration.